Locomotives (or other vehicles) typically include a prime mover that is powered by a fuel source to generate mechanical energy. In one example of a locomotive, mechanical energy generated by the prime mover may be converted to electrical energy that is used to power traction motors and other components and systems of the locomotive. In some examples, the prime mover may be a combustion engine that is fueled by diesel, gasoline, or other liquid petroleum distillates. In other examples the engine may additionally or alternatively utilize a gaseous fuel, such as natural gas.
In light of its favorable energy content, liquefied natural gas (LNG) may be used as a fuel source for a locomotive prime mover. Particularly for long-haul applications, it may also be desirable to utilize a tender car, also known as a fuel tender, for carrying one or more LNG storage tanks. Prior to injection into a locomotive's natural gas-fueled engine, LNG is typically vaporized into gaseous natural gas (CNG). Such vaporization is often accomplished by heating the LNG with a heat source.
In some examples such a heat source may take the form of a heat exchanger on board the locomotive. In these examples the LNG may be transferred from the tender car to the heat exchanger on the locomotive across an interface between the tender car and the locomotive. Such an interface, however, requires suitable cryogenic hosing, cryogenic coupling components, and associated design constraints and maintenance requirements. Transferring LNG across such an interface also creates the potential for LNG leaks.
In other examples, a heat exchanger may be located on board the tender car. Heated cooling fluid from the locomotive engine may be transferred from the locomotive to the heat exchanger on the tender car across an interface. However, as with transferring LNG across an interface, this configuration requires additional insulated hosing and coupling components that present design challenges and risks. Additionally, LNG storage tanks typically generate boil-off gas that may accumulate in the tank. To avoid excess pressure build up, such boil-off gas is typically vented from the storage tanks to atmosphere. Such venting of natural gas may raise environmental concerns.
The locomotive engine may also enter an idle mode when power for the locomotive propulsion system is not required. Nevertheless, instead of entering a shutdown mode, the locomotive engine may continue to idle to generate electricity needed by components and/or systems on board the locomotive. Such idling may produce undesirable exhaust emissions and reduce overall operating efficiencies.